Insulin degrading enzyme (IDE) is an evolutionarily conserved, 110 kDa metalloprotease that is involved in the clearance of insulin and amyloid ? (A?). Accumulating genetic evidence in rodents and humans strongly support the role of IDE in the progression of type 2 diabetes mellitus and Alzheimer's disease. Thus, it is vital to understand the functions, catalytic mechanism, and regulation of IDE from a molecular perspective to develop viable IDE-based therapeutic strategies. We have solved the structures of human IDE in complex with insulin, A?, and other functionally relevant substrates such as natriuretic peptides and proinflammatory chemokines, CCL3/CCL4. IDE has two 55 kDa domains, which form an enclosed catalytic chamber to entrap its substrates. Our structural and biochemical analyses reveal how IDE uses an enclosed catalytic chamber to selectively recognize the global features of its substrates. The long-term goal of this research is (1) to delineate the function(s) of IDE and the mechanism(s) of its regulation and (2) to elucidate the role of IDE in human diseases. The objectives of this application are to understand (1) the molecular basis for the open-closed conformational switch and dynamics of IDE during catalysis and (2) the molecular mechanism for the regulation of IDE. In addition, we will develop potent chemical modulators of IDE to be used as potential therapeutic agents and as tools to address the biological functions of this enzyme. The central hypothesis is that the open-closed conformational switch of IDE is the key regulatory step of IDE that is subject to allosteric regulation by dimerization, posttranslational modifications, cellular factors, and chemical modulators. The rationale for the proposed research is that understanding the regulation and functions of IDE and developing small chemical modulators of IDE will ultimately allow us to better design IDE-based therapeutic strategies specific to certain human diseases such as diabetes, Alzheimer's disease, and inflammation. Guided by our preliminary data, we will study the regulation and functions of IDE in three specific aims: in Aim 1, we will use single molecule Forster resonance energy transfer analyses to address the conformational switches and dynamics that occur during catalysis of IDE and to determine how the catalysis of IDE is regulated. Aim 2 is to use two distinct screening methods to develop potent small molecule compounds that can modulate the activity of IDE and use such compounds to address the biological functions of IDE. Aim 3 is to combine structural, biochemical, and mutational studies to address the molecular basis for the regulation of IDE by dimerization, physiologically relevant cellular factors such as intermediate filament proteins, nestin and vimentin, and by posttranslational modifications such as phosphorylation and acetylation. The proposed research is significant because it will generate new insights in the dynamics and regulation of a key enzyme involved in diabetes and Alzheimer's disease and because it will also lead to the discovery of new chemical leads that can potently modulate this enzyme. The proposed research is innovative because it employs biophysical, biochemical, cellular, and medicinal chemical approaches to investigate the regulation and functions of IDE.